Kurzbeschreibung (Abstract)

This paper describes the optimization of the heater design used in an electro-thermal pseudo-bimorph micro actuator. Pseudo bimorph is a kind of micro actuator where current runs through a loop of released structure consisting of a hot arm and a cold arm. Current is passed through the hot arm using a heating element which causes high current densisty. The hot arm heats up because of joule heating and expands. This causes in plane deflection of the actuator in a direction perpendicular to the length of the arms. The actuator is made of polymer SU-8, a negative photo resist which has a high coefficient of thermal expansion (CTE) up to 54×10-6. The actuator is fabricated on a FR-4 substrate which is a typical printed circuit board material which has better adhesion to SU-8 as compared to silicon. Nickel is used as the heating element. The actuator can be taken to a maximum temperature of 150°C.

The task of this project is the optimization of the heater design to achieve uniform heat distribution in the hot arm which in turn would create large in plane deflection and low out of plane deflection.Currently a evenly spaced meandered structure is being used. A reference design of the actuator is taken and the heater is built on this design. Design is done using electro-thermo-mechanical simulation in ANSYS Workbench .A total of four masks have been drawn using AutoCAD. The fabrication process is provided using surface micromachining processes. The fabrication was not done because of technical issues in the clean room.

Four heater design types: Simple bend, Meander, Vertical Meander and Double Meander have been simulated on ANSYS and uniform temperature distribution has been achieved by making variations to the designs. The in plane and out of plane motion achieved by using different kinds of designs has been noted. From the research it has been found that the double meander heated structure with varying element size across the hot arm and minimum width and thickness provides the best in plane deflection and very little out of plane deflection. The variation of element size of the double meander structure is plotted along the length of the hot arm. The Vertical meander provides an in plane deflection of 106 µm while there is a large 104 µm out of plane deflection making it unsuitable for in plane deflection. The double meander heating structure provides an in plane deflection of 145 µm while there is only 7 µm out of plane deflection. The Meander heating structure provides an in plane deflection of 141 µm which is a little lower than that of the double meander. The out of plane deflection was however significantly higher at 24 µm.

Design and fabrication of electrothermal pseudo-bimorph actuators with an improved performance

Sprache:

Englisch

Kurzbeschreibung (Abstract):

This paper describes the optimization of the heater design used in an electro-thermal pseudo-bimorph micro actuator. Pseudo bimorph is a kind of micro actuator where current runs through a loop of released structure consisting of a hot arm and a cold arm. Current is passed through the hot arm using a heating element which causes high current densisty. The hot arm heats up because of joule heating and expands. This causes in plane deflection of the actuator in a direction perpendicular to the length of the arms. The actuator is made of polymer SU-8, a negative photo resist which has a high coefficient of thermal expansion (CTE) up to 54×10-6. The actuator is fabricated on a FR-4 substrate which is a typical printed circuit board material which has better adhesion to SU-8 as compared to silicon. Nickel is used as the heating element. The actuator can be taken to a maximum temperature of 150°C.

The task of this project is the optimization of the heater design to achieve uniform heat distribution in the hot arm which in turn would create large in plane deflection and low out of plane deflection.Currently a evenly spaced meandered structure is being used. A reference design of the actuator is taken and the heater is built on this design. Design is done using electro-thermo-mechanical simulation in ANSYS Workbench .A total of four masks have been drawn using AutoCAD. The fabrication process is provided using surface micromachining processes. The fabrication was not done because of technical issues in the clean room.

Four heater design types: Simple bend, Meander, Vertical Meander and Double Meander have been simulated on ANSYS and uniform temperature distribution has been achieved by making variations to the designs. The in plane and out of plane motion achieved by using different kinds of designs has been noted. From the research it has been found that the double meander heated structure with varying element size across the hot arm and minimum width and thickness provides the best in plane deflection and very little out of plane deflection. The variation of element size of the double meander structure is plotted along the length of the hot arm. The Vertical meander provides an in plane deflection of 106 µm while there is a large 104 µm out of plane deflection making it unsuitable for in plane deflection. The double meander heating structure provides an in plane deflection of 145 µm while there is only 7 µm out of plane deflection. The Meander heating structure provides an in plane deflection of 141 µm which is a little lower than that of the double meander. The out of plane deflection was however significantly higher at 24 µm.